Using CO2 Efflux Rates to Indicate Below-Ground Growing Seasons by Land-use Treatment

Abstract

CO 2 efflux rates are affected by vegetation type, temperature, and soil surface conditions, and serve as an indicator of the length of the below-ground biological and microbial growing season. This study determined the effect of three land-use treatments on CO 2 efflux and growing season lengths in Southeast Virginia on two forested mineral soil wetlands. CO 2 efflux, soil temperature, and soil moisture were measured 24 times in 18 months at plots representing forest, early successional field, and bare ground landuse treatments. CO 2 efflux differed (p < 0.05) by treatment in the order forest > field > bare ground. CO 2 efflux was higher in hardwood-than conifer-dominated forest and higher in bare ground plots that were not inundated. Appreciable CO 2 efflux took place even once leaves had fallen off deciduous trees, and most of the CO 2 efflux appeared to be from vegetation rather than microbial sources during that period. Variability in CO 2 efflux was best described by the interaction between soil temperature and soil moisture (R 2 = 0.32) (p < 0.05). The below-ground growing season indicated by appreciable CO 2 efflux was similar to that indicated by soil temperatures above 5°C measured at 50 cm, the regulatory reference depth. The CO 2 efflux growing season was 365 days in the forest but was 9-16 days shorter in the field and 21-78 days shorter in the bare ground land-use treatment plots. These data can be used to modify the regulatory growing season definition in forested thermic wetlands and to reflect the environmental variation caused by different land uses.